Normal hydration can be important for health and wellbeing. Even small losses of body water can have a negative effect on muscle strength, endurance and maximal oxygen uptake, so it can be important to quickly, accurately, and continuously measure the hydration level of a human or animal host.
For example, hydration may be measured in a laboratory to test the effects of sports drinks, diets or exercise sessions, in a clinical environment to ensure the wellbeing of patients, by the military to evaluate whether personnel can fulfill active duties while remaining healthy, at major sporting events to ensure that athletes achieve their performance potential, or in a home setting to monitor if a family member, particularly an elderly person or child, is drinking a sufficient amount of fluid.
Hydration can be measured by, for example, acute changes in body mass, blood tests to evaluate hemoglobin concentration, sodium concentration or osmolarity, urine tests, or saliva flow rate, osmolarity or composition.
The practicalities of monitoring hydration levels to promote health and wellbeing are difficult due to the dynamic state of hydration and differences in how individuals respond to fluid gains and losses.